[TriEmbed] Need simple 1A controlled current power supply

[Rodney Radford]

I have ordered from Pololu for years and have been a promoter of them as
well and not sure why I didn't think to check there.

I found what I needed and just ordered it:

https://www.pololu.com/product/2857

Thanx

On Mon, Sep 26, 2016 at 3:55 PM, Dwight Morgan <dwight.w.morgan at gmail.com>
wrote:

> Shane sent out a resource site awhile back called pololu.com that might
> have what you need. I'm not sure but you could take a look.
>
>
> Sent from my iPad
>
> > On Sep 26, 2016, at 8:29 AM, Rodney Radford via TriEmbed <
> triembed at triembed.org> wrote:
> >
> > For the Southeastcon 2017 hardware robotics competition, one of the
> requirements is to be able to switch on and off a magnet field.
> >
> > The field is defined as number of turns, diameter, core, and the current
> - 1A - through it.  I need a simple (and cheap) way to implement this.  I
> will be building 8x of these for the competition and each school will be
> building one for their trial runs, so keeping it cheap and simple is better
> than elegant and higher cost.
> >
> > Initially I was planning on a very simple solution - a MOSFET switching
> current to the coil in series with a power resistor to drop the voltage.
> At first this was a 5 ohm, 5W power resistor (since the coil is below 0.1
> ohm), but then that changed to a 12 ohm, 12W power resistor as I switched
> over to using 12v to power everything since I needed that for the relays
> anyway (for another part of the design).
> >
> > This works, and is cheap and easy to build and if the coil is only on
> for a few seconds at a time, this is a great solution. However, a change in
> the contest stated that the coil is initially powered on (so robots can use
> it to navigate to the coil) and if the robot fails, it could be on for the
> full duration of the 5 minute competition.
> >
> > I tested this last night and it does work, but 12w through even a metal
> power resistor is HOT after about 30 seconds.  I would hate to use this for
> 5 minutes.  The cost is good - below $2 for the MOSFET and power resistor -
> but I am looking to see if there is a better solution.
> >
> > Some ideas considered:
> > * use a lower voltage - would work, but I would need a lower voltage 1A
> supply
> > * use a switched regulator - get the lower voltage *and* ability to
> control it
> > * others?
> >
> > Any thoughts / suggestions?
> >
> > Btw, I will be bringing this in to the next meeting (next R&A/TAR and
> next Triembed) to show the progress on the hardware and software design.
> Most of it is done now and I hope to finish it in the next few days.
> >
> > On another issue - I watched a couple Eagle videos this weekend and was
> able to complete the schematic capture for the board and even routed a PCB.
> The routes were done with the auto-router and they were ugly, but
> functional. Not sure if I will just route it myself, or route some and let
> the autorouter finish, etc, but I need to investigate the design rules for
> the fab house first to verify I have spacings, hole sizes, trace widths,
> etc are correct before I dump too much more time into it.
> >
> > Thanx,
> > Rodney
> >
> > _______________________________________________
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>
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